1. Field of the Invention
The present invention relates to an electric flash device and a camera, which control flash duration.
2. Description of the Related Art
As a light controlling method of an electric flash device, a method in which the electric flash device is pre-flashed prior to an actual-flash and luminous intensity and flash duration of the actual-flash are controlled according to subject brightness when the pre-flash is performed is conventionally known.
The following two methods are also known as flash methods of the electric flash device.
(1) a method of flashing immediately after a shutter curtain is fully opened (what is called a discrete flash)
(2) a method of repeating consecutive flashes so that a uniform exposure amount is obtained all over a screen with a shutter being in a state of slit traveling (what is called an FP flash)
Generally, the flash duration of the discrete flash is approximately 1 mS and the flash duration of the FP flash is approximately 200 to 300 mS.
The same flash method is conventionally employed both for the actual-flash and for the pre-flash in the electric flash device in order to simplify an arithmetic operation relating to light control conditions of the actual-flash. In other words, when the actual-flash is the FP flash, the pre-flash is always the FP flash and when the actual-flash is the discrete-flash, the pre-flash is always the discrete-flash.
Incidentally, the flash duration of the FP flash is longer than that of the discrete flash and furthermore, repeated switching control of the flashing is required. As a result, the FP flash consumes more luminous energy than the discrete flash. Therefore, when the FP flash is performed as the pre-flash, there exists a problem that much luminous energy is consumed by the electric flash device.
When the FP flash is performed as the pre-flash, there also exists a problem that the flash duration of the pre-flash becomes relatively long and therefore, more time is needed for performing photometry.
The above-described problems become critical problems particularly in consecutive photographing which requires flash illumination. More specifically, when the FP flash is performed as the pre-flash, the more time is needed for re-charging the luminous energy and the more time is required for performing the photometry of the pre-flash in the electric flash device. This results in lengthening time intervals of the consecutive photographing and reducing speed of a consecutive photographing.
The present invention provides an electric flash device and a camera in which the above problems are solved by selecting a discrete flash to work as a pre-flash.
The present invention is specifically explained as follows.
(1) The electric flash device according to the present invention is an electric flash device allowing selection between xe2x80x9can FP flash which repeats flashing at such time intervals that the repeated flashing is recognizable as flat lightxe2x80x9d and xe2x80x9ca discrete flashxe2x80x9d, and flashing synchronously with photographing by the camera, the electric flash device comprising: a pre-flash part for performing a pre-flash prior to photographing by the camera; a right condition obtaining part for obtaining from the camera information on a condition of a right amount of light determined according to subject brightness when the pre-flash is performed; and an actual-flash part for performing an actual-flash according to the information on the condition of the right amount of light which is obtained by the right condition obtaining part, the actual-flashing performed when the photographing by the camera is performed, wherein the pre-flash part performs the discrete flash including one flash or a plurality of flashes as the pre-flash, even when the FP flash is selected as the actual-flash.
(2) According to another aspect of the electric flash device of the present invention, the actual-flash part in the electric flash device described in (1) obtains from the camera information on a traveling condition of a shutter curtain for performing the photographing and, according to the condition of the right amount of light and the traveling condition which are determined by the discrete flash, determines a flashed-light waveform of the FP flash for performing the actual-flash.
(3) The camera according to the present invention is a camera which controls an electric flash device allowing selection between xe2x80x9can FP flash which repeats flashing at such time intervals that the repeated flashing is recognizable as flat lightxe2x80x9d and xe2x80x9ca discrete flashxe2x80x9d, the camera comprising: a photographing part for photographing a subject image; a pre-photometry part for performing photometry on subject brightness while controlling the electric flash device to perform a pre-flash, and determining a condition of a right amount of light for performing an actual-flash according to a result of photometry, prior to photographing by the photographing part; and a light controlling part for performing light control of the electric flash device to perform the actual-flash according to the condition of the right amount of light which is determined by the pre-photometry part, the light control performed when the photographing is performed by the photographing part, wherein when the FP flash is selected as the actual-flash, the pre-photometry part controls the electric flash device to perform the discrete flash as the pre-flash, including one flash or a plurality of flashes, and determines the condition of the right amount of light of the FP flash for performing the actual-flash according to the result of photometry on the subject brightness when the pre-flash is performed.
(4) According to another aspect of the camera of the present invention, the pre-photometry part in the camera described in (3), when the pre-flash is performed, notifies the electric flash device of a starting signal of the discrete flash the same number of times as the discrete flash is performed, and determines the right amount of light for the FP flash to perform the actual-flash according to an amount of light of the pre-flash which is calculated from the number of times the discrete flash is performed, and the photometry result.
(5) According to still another aspect of the camera of the present invention, the pre-photometry part in the camera described in (3), when the pre-flash is performed, obtains from the electric flash device information on the number of times the discrete flash is performed, and determines the right amount of light for the FP flash to perform the actual-flash according to an amount of light of the pre-flash which is calculated from the number of times the discrete flash is performed, and the photometry result.
In the electric flash devices and cameras as described above, when the FP-flash is selected as the actual-flash, the discrete flash including one flash or a plurality of flashes is performed as the pre-flash so that luminous energy required for performing the photometry can be reduced and time required for performing the photometry can be shortened.
Incidentally, the appropriate traveling condition(s) of the shutter curtain mentioned above may be, for example, a specific slit width, a specific shutter curtain speed, a specific aperture value, a specific ISO sensitivity, a specific flash duration, and so on. A value or values of one or more of these appropriate traveling conditions are obtained from the camera by the electric flash device. As for values, which are not obtained from the camera, using specified value(s) is preferred. Furthermore, a flashed-light waveform of the FP flash is preferably determined according to, for example, a frequency of flashes, duty which is a ratio of the flash duration to a flash quenching duration in one cycle, and the luminous intensity.